They are in alpha still, but you can buy a copy on the cheap and get all future versions free! The paid version now has Kerbin, It's moon, the Mun, and a planet way out far on an inclined orbit called Minmus. And monoliths to find, and moon arches.

The modding community has made rotating joints, satellite remote control networks, power systems, hydrolic pistons, cars, there is even a whole space plane module now (Though it's not very well implimented, but it's alpha.) You can even map planets with a satellite. Produces a nice jpg.